1. Field of the Invention
This invention relates to an improved fluid lock drive train for use with partially locking automotive differentials and the like.
2. Description of the Prior Art
A conventional bevel gear differential delivers equal output torque to both of its output shafts. Equal division of output torque permits each wheel connected to the output shaft to rotate at different speeds when required, for example, when the vehicle is turning a corner. This characteristic of delivering equal torque to each wheel of a vehicle is undesirable when one wheel has greater traction than the other, for example, when one wheel rests on dry pavement and the other wheel rests on a slippery surface. Both wheels have equal driving power applied thereto. That power is limited to whatever power is delivered to the wheel on the slippery surface. As a result, the wheel on the dry pavement receives very little power and the vehicle becomes stuck. Of course, both output shafts could be locked together so that the differential is, in effect, a locked differential. Obviously, this would eliminate the desirable aspects of the differential and make turning and handling very difficult on surfaces having good traction characteristics since both wheels would have to rotate as the same speed at all times.
To enable vehicles to operate on slipery surfaces, various types of so called partially locking or limited slip differential systems have been developed. A partially locked differential system permits drive power to be transferred to the wheel having good traction while still permitting normal differential action, which permits one wheel to rotate faster than another while the vehicle is making a turn.
An oil-operated system is disclosed in U.S. Pat. No. 4,084,654 entitled "PARTIALLY FLUID LOCKED VEHICLE DRIVE TRAIN", granted to Harold M. Dudek on April 18, 1978. That system uses oil both for partially locking a differential gear train and for cooling the differential gear train. A planetary gear drive for that system has all the component gears lying in a common plane and enclosed on opposite sides by closely abutting side plates which form chambers for the gears. The side plates are provided with oil passages which allow oil to enter into the gear teeth at points upstream from the meshing points of the gear teeth. The oil is carried by the gear teeth and squeezed between the intermeshing a close-toleranced gear teeth to provide fluid resistance to movement of the gears. The fluid resistance provides a partial fluid locking of the planetary drive train. The side plates are formed to fit closely against the gear ends and to form chambers which closely surround the peripheries of the gears. The planet gears used for the drive train are mounted on rigididly supported bearings so that the spacing of the planet gears with respect to the walls of the chambers are fixed.
As an example of a frictional prior art limited slip differential, the Detroit Automotive Division of Aspro, Inc., Warren, Michigan provides a gear-type mechanism which uses a pair of intermeshing roller type helical pinion gears. Each output axle is connected to one of a pair of coaxially aligned sun gears. Each pinion gear engages one of the sun gears to provide differential action. The geometry of the gears causes the pinion gears to move against the walls of their supporting pockets to develop rubbing friction between the gears and the pockets.